It has long been a common practice to administer chemical additives to cattle and other livestock to supplement feed rations, thereby providing a balanced diet, protecting the animals from disease, and stimulating growth. For example, administration of certain live bacteria, such as lactobacilli, can help restore optimal intestinal flora in animals such as cattle, especially after stressful situations such as transport to a feedlot. With regular administration, the lactobacilli may increase nutrient absorption efficiency and help control the proliferation of harmful microorganisms in animals' digestive tracts that could otherwise cause disease conditions that adversely affect rates of animal development and weight gain. Most commonly administered to cattle for such purposes are strains of Lactobacillus acidophilus, a microaerophilic lactic acid producer. While lactobacilli have been effective for promoting animal health, they suffer from physiological properties that make their storage and handling problematic.
Concentrated cultures composed of single or mixed strains of lactic acid bacteria have been prepared under batch fermenter conditions, concentrated to a smaller volume, and then placed in frozen or dried storage. However, the lactobacilli reportedly do not respond well to lyophilization, spray drying, or conventional frozen storage at -20.degree. C. Therefore, liquid nitrogen and ultra-cold freezers (-80.degree. to -100.degree. C.) have been preferred methods for maintaining the highest culture viability and activity. See: Klaenhammer, T. R., Our industry today, J. Dairy Sci. 65: 1339-1349, 1982.
For example, in the manufacture of a bacterial preparation for the prophylaxis of intestinal disturbances in poultry, the cultivated lactobacilli are deep-frozen (-70.degree. C.) or lyophilized; see U.S. Pat. No. 4,689,226 (column 4, line 64). Lactobacillus strains for human therapy are often provided in lyophilized form; see U.S. Pat. No. 4,839,281 (column 5, line 52).
U.S. Pat. No. 4,518,696 (Gehrman et al.) reports that dried, stabilized concentrates of Lactobacillus acidophilus have been administered to mammals in milk and other aqueous suspensions. Unless the suspension is to be stored and distributed under refrigerated conditions, such as with commercial acidophilus milk, it has reportedly heretofore been necessary to prepare the suspension immediately prior to use in order to be certain that a sufficiently high percentage of the cells administered remain viable at the time of administration. Lyophilized concentrates of lactobacilli have been prepared, but such dried cell concentrates are reportedly not adequately stable in aqueous suspension unless the suspension is refrigerated. The patent discloses the use of sunflower seed oil as a liquid suspending medium for dry lactobacilli, resulting in a slow suspension manifesting a high degree of cell stability at room temperature.
A commercially available lactobacillus feed additive concentrate for cattle, sold under the COBACTIN.RTM. trademark by Bio-Techniques Laboratories, Inc., Redmond, Wash., is a lyophilized material. The accompanying directions recommend mixing the lyophilized contents into cool water and keeping the liquid concentrate cool. The liquid concentrate is diluted in cool water and sprayed over livestock feed. If the liquid concentrate is not used immediately, it can reportedly be refrigerated for up to 10 days to prolong viability.
U.S. Pat. No. 4,910,024 (Pratt) in particular, describes a method and apparatus for administering live bacteria such as lactobacilli as feed additives to livestock and poultry. This patent reports that lyophilizing the bacteria greatly extends the shelf life of commercially packaged bacteria formulations; however, such packaging still does not solve the problem of maintaining the bacteria in a live state and delivering them to large numbers of animals in proper dosages after the package is opened. Without some means of extending viability, bacteria from an unopened package must reportedly be properly diluted and presented to the animals within a very short time after opening the package, which is time-prohibitive and impractical in large feedlots. To overcome these difficulties, the lyophilized bacteria are suspended in an aqueous medium at a temperature (generally between 36.degree. to 50.degree. F.) that is maintained sufficiently low to reportedly inhibit anabolic or catabolic processes that reduce viability.
Lyophilized lactobacilli, such as the type used in Pratt, are typically stored in a suitable dry carrier including a flow agent such as sugar, and cryoprotectants such as monosodium glutamate and nonfat milk solids. These diluents add a significant amount of solids to the packaged concentrate. The significant amount of solids associated with the lyophilized bacteria makes it difficult, if not impossible, to maintain a homogenous suspension of the concentrate without constant or intermittent agitation, because the solids settle out of the suspension. Settling of the solids is undesirable because the sediment clogs delivery and transport lines, which must then be cleaned frequently. A uniform suspension of bacteria is necessary to ensure that the doses that are delivered to the livestock contain predictable and consistent cell counts. As reported in Pratt, without constant or intermittent agitation, the suspensions can become nonuniform in as little as 15 minutes.
Furthermore, lyophilization is a harsh process for the bacteria cells to survive, often resulting in a 40% to 60% loss of viability. Another disadvantage of lyophilization is that the process is energy-intensive. The costs of the energy contribute to the overall cost of the lyophilized bacteria.